Ignition devices

ABSTRACT

1,075,321. Ignition systems. LABORATOIRE D&#39;ELECTRONIQUE ET D&#39;AUTOMATIQUE DAUPHINOIS (L.E.A.D.), and APPAREILLAGE THERMOFLEX, ETABLISSEMENTS J.M. DARD. March 23, 1965 [March 24, 1964], No. 12257/65. Heading F1B. An ignition device for igniting gas or oil burners comprises an arc gap member 11 placed in the vicinity of a burner to be ignited and fed on the one hand by an alternating low voltage source 12 and on the other hand by a high voltage pulse generator which is itself fed by the alternating voltage source and means dispersed between the member and the source for isolating the source from the high frequency current components of the arcs produced across the element. The isolating means may comprise at least one high frequency choke coil 16 in series between one electrode of the arc gap member and one terminal of the low voltage source and a filter capacitor 15 may be connected in series with the choke. The isolating means may comprise a second high frequency choke coil and a second filter capacitor between the other electrode of the arc gap member and the other terminal of the low voltage source. A switch may be provided for disconnecting the alternating voltage source from the pulse generator after current has flowed through the member for a predetermined period of time. Reference is made to delayed action by electric, electro-hydraulic or electro-pneumatic relay. In Fig.4 (not shown) ionization causes the resistor of the blade 36 to continue to be traversed, even when no arc is present across the gap 11, by a small current capable of generating sufficient heat to cause the blade 36 to close the switch 35 and open the switch in series with the primary winding 17. It is stated that the capacitors 15 may be replaced by resistances whose self-inductances block the high frequency components.

y 1968 F. MAYER IGNITION DEVICES Filed March 22, 1965 fl ng, O 19 -15 Q /3 1/ fi fiyer I i Amm ys I A r22 E7 25 I 79 J 20 i /8 United States 3,384,440 IGNITION DEVICES Ferdy Mayer, Grenoble, France, assignor to Laboratoire diElectronique et dAutomatique Dauphinois (LEAD) and Appareillagc Thermofiex (Ets. .1. M. Dal-d), Grenoble, Isere, France, both corporations of France Filed Mar. 22, 1965, Ser. No. 441,450 Claims priority, application France, Mar. 24, 1964, 968,463 Claims. (Cl. 431-66) ABSTRACT OF THE DISCLOSURE This invention relates to ignition devices and particularly to devices for lighting gas or oil burners or similar units.

According to this invention, the ignition device comprises an arc-producing element placed in the vicinity of the burner and fed on the one hand, by the output of an alternating voltage low voltage source and, on the other hand, by the output of a high-voltage pulse generator which is itself fed by the output of said alternating voltage source, said device being characterised in that it comprises means placed between said element and said source for isolating said source from the high frequency current components of the arcs produced across said element.

It is an object of this invention to provide certain improvements for such devices, which improvements serve to assure the protection of these burners and to monitor their flame.

These and other objects, features and characteristics of the present invention will become more readily apparent from the following detailed description when taken together with the attached drawings, in which:

FIG. 1 is a schematic diagram of one embodiment of the present invention;

FIG. 2 is a schematic diagram of a variation of the embodiment of FIG. 1;

FIG. 3 is a schematic diagram of the embodiment of FIG. 1 equipped with one improvement according to the invention; and

FIG. 4 is a schematic diagram of the embodiment of FIG. 1 equipped with another improvement according to the present invention.

According to the embodiment shown in FIG. 1, there is disposed, in a combustion chamber 10 and in proximity to a burner to be ignited (not shown) a fixed electrode spark gap 11. This spark gap is fed by an alternating low voltage source 12 through the intermediary of the fine-wire secondary winding 13 of a step-up transformer 14 and, in each lead to gap 11, is connected to a capacitor 15 in series with a high frequency choke coil 16. The source 12, which could be constituted by an electrical power mains, also feeds the primary winding 17 of a low voltage transformer 18 whose secondary winding 19 is connected to the thick-wire primary winding 20 of step-up transformer 14 through the intermediary of an inductance 21 and an auxiliary fixed-electrode spark gap 22. The secondary winding 19 of transformer 18 also Cir feeds a capacitor 23 through inductance 21. A protective capacitor 24 is connected in parallel across the series circuit of principal spark gap 11 and secondary 13.

At the start of a cycle of the voltage output from source 12, the voltage level is insufficient to produce a spark across gap 22 and no arc is established between the electrodes of principal spark gap 11. During this period capacitor 23 becomes charged.

At a given point in this cycle, the voltage output from source 12 becomes sufficient to trigger a spark between the electrodes of spark gap 22. This places capacitor 23 in short circuit and causes it to discharge abruptly through primary 20 of step-up transformer 14. This produces a high-voltage pulse in secondary 13, which pulse passes through capacitor 24 and is suflicient to trigger a spark between the electrodes of spark gap 11. Transformer 14 constitutes, in effect, a Tesla coil and the spark appearing between electrodes of spark gap 11 represents a Tesla-type discharge. This spark is reheated by the low voltage applied across the spark gap directly from source 12, is thereby prolonged during a portion of, or during the entire duration of, the instant half-cycle of the output voltage from source 12, and is capable of bringing about the ignition of the fuel issuing from the burner with which spark gap 11 is associated. The spark appearing across gap 11 thus has the form of a high energy density are which is capable of efficiently igniting relatively heavy fuels. The generation of a satisfactory arc requires, of course, that for a given output voltage from source 12 and a given type of fuel, the electrodes of spark gap 11 be separated from one another by an appropriate distance to give the spark gap a suitable length.

The principal function of capacitor 24 is to act as a short circuit path for the train of high frequency waves generated by the high voltage pulse, while the choke coils 16 serve to isolate the high-frequency components of the high voltage pulses from the supply mains and capacitors 15 act as low-frequency and D.C. current limiters. Capacitors 15 could be replaced by any suitable type of impedances serving to limit the current to source 12. According to one preferred arrangement, these impedances could be constituted by a plurality of electrochemical capacitors connected in a series-aiding relation, or by wound resistances whose self inductances intervene to block the high frequency components of the spark.

FIG. 2 shows a variation of the above-described circuit in which the various elements are identical with, and have the same function as, the like-numbered elements of FIG. 1. The only difference presented by the FIG. 2 circuit resides in the fact that the device has been simplified by the elimination of capacitor 24 and by the placing of spark gap 11 in parallel across secondary winding 13.

FIGS. 3 and 4 show various improvements intended to complete and improve the above-described device.

Turning now to FIG. 3, there is shown a device which is identical with that of FIG. 1, with the addition of a switch 25 in series between source 12 and primary winding 17 and a bimetallic protective element 26 associated with a heating resistance placed in series between source 12 and spark gap 11, said protective element being mechanically connected to said switch to open the latter when the heat generated by the heating resistor causes the bimetallic element to deflect to a predetermined degree.

After the high voltage pulses across transformer secondary 13 generate an arc across spark gap 11, in the manner described above in connection with FIG. 1, the low voltage current flowing through the resistance associated with element 26 achieves a relatively high average value, of the order of ma. for example. This current is used to detect the presence of an arc in that it causes sufficient heat to be produced by the resistance to deflect element 26 to a point where it opens switch 25, deactivating the circuit feeding auxiliary spark gap 22. This result is desirable because the presence of an arc across gap 11 generates a flame and this renders the production of further high voltage arc-producing pulses unnecessary, and because the opening of switch 25 protects the burner from further high-voltage sparks across gap 11. It should be understood that element 26 can be replaced by any other type of actuating means, such as a relay coil, if an instantaneous or time-delayed action is desired.

Turning now to FIG. 4, the ignition spark gap 11 is shown to be placed in the zone occupied by the flame of a burner 38, and the mains 12 are shown to also feed a protective relay 31 through the intermediary of a coldcathode thyratron 32 the control electrode of which re ceives its input from a potentiometer formed by spark gap 11 and a resistor 33 connected in parallel with a capacitor 34. A normally open switch 35 is connected in series between gap 11 and resistor 33 and is operated by a temperature-sensitive bimetallic blade 36 having an associated heating resistance connected between the source 12 and spark gap 11. A normally closed switch is connected in series between mains 12 and primary 17 and is mechanically linked to be operated by blade 36. All of the other circuit elements are identical with the likenumbered elements of FIG. 1. When the burner becomes ignited, its flame produces an ionization of the gas surrounding the electrodes of gap 11. This ionization causes the resistor of blade 36 to continue to be traversed, even when no arc is present across gap 11, by a small current capable of generating sufficient heat to cause blade 36 to close switch 35 and to open the switch in series with primary 17. The closing of switch 35 causes a thyratronenergizing voltage to be applied to the thyratron control electrode, generating a current flow through thyratron 32 for energizing relay 31. Relay 31 will continue to be energized, by the current flowing through thyratron 32, as long as the burner flame continues to surround gap 11 with an ionized atmosphere. At the same time, the heat applied to blade 36 causes it to open the switch in series with primary 17, thus preventing further sparks from being initiated across gap 22, and hence across gap 11. When the flame disappears, the current through the heating resistor of blade 36 become eflectively null, permitting switch 3-5 to open, thereby removing the energizing voltage from the thyratron control electrode. This causes the flow of thyratron current to cease, with the result that relay 31 become de-energized. Relay 31 is provided with switches which operate, upon the de-energization of this relay, certain protective systems (not shown). For example, one such switch could operate to turn off the supply of fuel to burner 30 and to disconnect mains 12 when the relay is de-energized. These systems must be manually re-activated when it is desired to re-ignite the burner and must be held in their activated condition until relay 31 once again becomes energized.

While several preferred embodiments of the present invention have been shown and described in detail herein, it should be appreciated that many variations and modifications can be made without departing from the spirit thereof, and that the coverage of this invention should therefore be limited only by the scope of the appended claims.

What I claim is:

1. In combination with a burner, an ignition device for said burner comprising: an alternating low-voltage source; a high-voltage Tesla pulse generator; an are producing element composed of a pair of suitably spaced electrodes; circuit means connected between said element and both said source and said generator for applying the output voltages from said source and said generator across said electrodes; and high-frequency isolating means connecting directly between said element and said source for isolating said source from the high frequency current components of the discharge produced across said element and adapted to pass low-frequency current components through said element.

2. A device as defined in claim 1 wherein said isolating means comprises at least one high-frequency choke coil connected in series between one side of said element and one of the outputs of said source.

3. A device as defined in claim 2 wherein said isolating means further comprises at least one filter capacitor connected in series with said coil.

4. A device as defined in claim 2 wherein said isolating means further comprises a second high-frequency choke coil and a second filter capacitor connected in series with one another and between the other side of said element and a second one of the outputs of said source.

5. An arrangement as defined in claim 1 further comprising current detecting means connected to said element for disconnecting said source from said generator after current has flowed through said element for a predetermined period of time.

6. A device as defined in claim 5 wherein said current detecting means comprises a heating resistor connected in series between said element and said source and a thermosensitive member which changes shape as a result of changes in its temperature, said member being mounted in heat exchange relation with said resistor.

7. A device as defined in claim 6 wherein said detecting means further comprises a normally closed switch connected in series between said source and said generator, and control means connected between said thermosensitive member and said switch for opening the latter in response to a predetermined current flow through said resistor.

8. A device as defined in claim 7 wherein said control means is constituted by a direct mechanical linkage between said member and said switch.

9. A device as defined in claim 7 wherein said control means comprises: an electronic switch having a principal current flow path and a control input; an input circuit connected to said control input to trigger the flow of current in said path; a relay coil connected in series with said path and mounted to open said normally closed switch when current flows in said path; a normally open switch connected between said element and said input circuit; and link means connected between said thermosensitive member and said normally open switch for closing the latter when said member has been heated to a predetermined temperature by the current flowing through said resistor thereby connecting said arc-producing element to said input circuit to permit current flowing through said element to cause said input circuit to trigger the flow of current in said path.

10. A device as defined in claim 9 wherein said burner is placed to have the fuel flowing therefrom ignited by the arcs produced across said arc-producing element and to have its ionized exhaust gasses envelope said element so that, after the production of arcs has been terminated by the opening of said normally closed switch, a suflicient ionization current flows across said element to maintain said thermosensitive member at least at said predetermined temperature.

References Cited UNITED STATES PATENTS 1,688,126 10/1928 Metcalfe 158-28 1,880,871 10/1932 Denison 15828 1,920,115 7/1933 Spear. 2,238,892 4/1941 Fanger 158-28 FOREIGN PATENTS 819,099 8/ 1959 Great Britain.

JAMES W. WESTHAVER, Primary Examiner. 

